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00:00:00 --> 00:00:03 Anna: On Thursday, a spacecraft the size of a
00:00:03 --> 00:00:05 small car will turn around in deep space,
00:00:06 --> 00:00:08 point three of its thrusters at its
00:00:08 --> 00:00:11 destination and fire them for an hour and a
00:00:11 --> 00:00:13 half without stopping. It has been travelling
00:00:13 --> 00:00:16 for two years. Now it has to slow
00:00:16 --> 00:00:16 down.
00:00:17 --> 00:00:20 Avery: It's ESA's HERA, and last week it
00:00:20 --> 00:00:23 saw its target for the first time. A single
00:00:23 --> 00:00:25 bright dot that happens to be the first
00:00:25 --> 00:00:27 object in the solar system humans have
00:00:27 --> 00:00:28 deliberately moved.
00:00:29 --> 00:00:32 Anna: Welcome to Astronomy AstroDailyPod. I'm Anna.
00:00:32 --> 00:00:35 Avery: And I'm avery. It's Tuesday the 13th of
00:00:35 --> 00:00:38 October 2026. Coming up,
00:00:38 --> 00:00:40 solar Orbiter follows a kink in the solar
00:00:40 --> 00:00:43 wind all the way home. A supernova seen in
00:00:43 --> 00:00:46 the year 1181 turns out to be strung with
00:00:46 --> 00:00:49 pearls. And Webb reads the rubble of
00:00:49 --> 00:00:50 worlds colliding.
00:00:50 --> 00:00:53 Anna: Plus a, uh, Mars rover with a brand new
00:00:53 --> 00:00:55 driving record. And the Moon meets
00:00:55 --> 00:00:58 Antares in the skywatch. Let's get
00:00:58 --> 00:01:01 into it. Let's start with where Hera
00:01:01 --> 00:01:04 is, because what happens on Thursday only
00:01:04 --> 00:01:06 makes sense once you know how fast it's
00:01:06 --> 00:01:09 going. Hera launched on a Falcon 9
00:01:09 --> 00:01:12 from Cape Canaveral on 7 October 2024,
00:01:12 --> 00:01:14 a couple of days ahead of Hurricane Milton.
00:01:14 --> 00:01:17 It couldn't wait. It had a date with Mars
00:01:17 --> 00:01:19 and missing that window would have added
00:01:19 --> 00:01:21 years to the trip.
00:01:22 --> 00:01:24 Avery: And, um, that Mars flyby came in March last
00:01:24 --> 00:01:27 year. Hera swung past the planet,
00:01:27 --> 00:01:29 grabbed some pictures of the little moon
00:01:29 --> 00:01:32 Deimos on the way through and came
00:01:32 --> 00:01:35 out bent onto a new path and moving faster.
00:01:36 --> 00:01:39 Anna: Since then, ESA says Isaac Newton has
00:01:39 --> 00:01:41 done most of the driving, long stretches of
00:01:41 --> 00:01:44 coasting with a pair of deep space manoeuvres
00:01:44 --> 00:01:47 to tidy things up. Right now, Hera
00:01:47 --> 00:01:49 is moving at more than 12 kilometres per
00:01:49 --> 00:01:52 second relative to Earth, crossing out past
00:01:52 --> 00:01:55 the orbit of Mars and closing on the orbit of
00:01:55 --> 00:01:57 Avery: its target, which is Didymus.
00:01:58 --> 00:02:00 Anna: Didymus is a, uh, near Earth asteroid, about
00:02:01 --> 00:02:04 780 metres across and it has
00:02:04 --> 00:02:06 a moon. Dimorphos is roughly
00:02:06 --> 00:02:09 150 metres across and circles
00:02:09 --> 00:02:11 Didymus about every 12 hours.
00:02:12 --> 00:02:15 And on 26 September 2022,
00:02:15 --> 00:02:18 NASA's DART spacecraft flew straight into
00:02:18 --> 00:02:21 Dimorphos A at about 6 kilometres per second.
00:02:21 --> 00:02:22 Avery: On purpose?
00:02:23 --> 00:02:26 Anna: Very much on purpose. It was the first real
00:02:26 --> 00:02:29 test of whether you can nudge an asteroid by
00:02:29 --> 00:02:31 hitting it. And it worked.
00:02:32 --> 00:02:34 Telescopes on Earth showed the orbit of
00:02:34 --> 00:02:36 Dimorphos around Didymos had shortened by
00:02:36 --> 00:02:39 about 33 minutes. ESA likes to point
00:02:39 --> 00:02:42 out that Dimorphos is the first object in the
00:02:42 --> 00:02:44 solar system to have been changed by human
00:02:44 --> 00:02:44 action.
00:02:45 --> 00:02:48 Avery: So Last Wednesday the 7th, exactly two
00:02:48 --> 00:02:50 years after launch, HERA got its first
00:02:50 --> 00:02:52 look from about
00:02:52 --> 00:02:55 236 kilometres away.
00:02:55 --> 00:02:57 Didymos showed up in the camera as a dot
00:02:58 --> 00:03:00 smaller than a single pixel. The team had
00:03:00 --> 00:03:03 to combine several images and do careful
00:03:03 --> 00:03:05 brightness analysis just to pick it out from
00:03:05 --> 00:03:06 the background stars,
00:03:06 --> 00:03:09 Anna: which is a lovely moment because until then,
00:03:09 --> 00:03:11 Didymos was a calculated point in space.
00:03:12 --> 00:03:14 Now the spacecraft can actually see where
00:03:14 --> 00:03:15 it's going.
00:03:15 --> 00:03:17 Avery: And now it has to stop.
00:03:18 --> 00:03:21 HERA is closing on Didymos, far too fast to
00:03:21 --> 00:03:23 arrive. So on Thursday the 15th,
00:03:24 --> 00:03:26 early in the European morning, the spacecraft
00:03:26 --> 00:03:29 will rotate so that its ring of orbit control
00:03:29 --> 00:03:32 thrusters faces the asteroids. Three
00:03:32 --> 00:03:34 of those hydrazine thrusters fire together
00:03:34 --> 00:03:37 and keep burning continuously for
00:03:37 --> 00:03:38 93 minutes.
00:03:39 --> 00:03:42 Anna: That's the first braking manoeuvre, BRM1,
00:03:42 --> 00:03:44 and it takes a few hundred metres per second
00:03:44 --> 00:03:47 off Hera's speed relative to the asteroids.
00:03:48 --> 00:03:51 That doesn't sound like much against 12
00:03:51 --> 00:03:53 kilometres a second relative to Earth.
00:03:53 --> 00:03:56 But the number that matters is the speed
00:03:56 --> 00:03:58 relative to the target, and that is the one
00:03:58 --> 00:04:01 that has to come down to almost nothing.
00:04:01 --> 00:04:04 Avery: It's tricky flying too. While the big
00:04:04 --> 00:04:06 thrusters push, the small reaction control
00:04:06 --> 00:04:08 thrusters on the corners of the spacecraft
00:04:09 --> 00:04:11 have to hold it pointing in exactly the right
00:04:11 --> 00:04:14 direction for an hour and a half. The team
00:04:14 --> 00:04:16 ran a short Test burn on 2 October before
00:04:16 --> 00:04:18 building the full command sequence.
00:04:19 --> 00:04:21 Anna: And for our Australian listeners, there's a
00:04:21 --> 00:04:24 nice local detail. As soon as the burn
00:04:24 --> 00:04:27 ends, ESO's Flight Dynamics team will pick up
00:04:27 --> 00:04:30 HERA's signal through one of its 35 metre
00:04:30 --> 00:04:33 deep space antennas at Ah, New Norcia in
00:04:33 --> 00:04:35 Western Australia, north of Perth,
00:04:35 --> 00:04:38 Flight Dynamics engineer Francesco Castellini
00:04:38 --> 00:04:41 says that's when the the really hard work
00:04:41 --> 00:04:41 starts.
00:04:42 --> 00:04:44 Using the spacecraft's own navigation data,
00:04:44 --> 00:04:47 plus the ranging and Doppler shift carried in
00:04:47 --> 00:04:50 the radio signal itself to check the burn
00:04:50 --> 00:04:52 went in the right direction and by the right
00:04:52 --> 00:04:52 amount.
00:04:52 --> 00:04:55 Avery: On timing, ESA hasn't published the
00:04:55 --> 00:04:58 exact minute. Early Thursday morning
00:04:58 --> 00:05:01 in Europe is Thursday afternoon or evening on
00:05:01 --> 00:05:04 Australia's east coast and late Wednesday
00:05:04 --> 00:05:07 night or the small hours of Thursday in North
00:05:07 --> 00:05:07 America.
00:05:08 --> 00:05:10 Anna: Then On Thursday the 22nd comes
00:05:10 --> 00:05:13 BRM2, a shorter burn of about
00:05:13 --> 00:05:16 31 minutes that does most of the remaining
00:05:16 --> 00:05:18 slowing. And it's deliberately designed to
00:05:18 --> 00:05:20 mop up any error from the first one.
00:05:21 --> 00:05:23 After that, three smaller transition
00:05:23 --> 00:05:25 manoeuvres at the end of the month bring
00:05:25 --> 00:05:27 hera's speed relative to Didymos down to
00:05:27 --> 00:05:28 almost zero.
00:05:29 --> 00:05:31 Avery: Here's the question. I suspect plenty of
00:05:31 --> 00:05:34 listeners are asking. Dart worked.
00:05:34 --> 00:05:36 We measured it. Why send a second
00:05:36 --> 00:05:39 spacecraft all the way out there to look at a
00:05:39 --> 00:05:41 rock we already know we moved?
00:05:41 --> 00:05:44 Anna: Because it moved isn't enough to build a
00:05:44 --> 00:05:47 planetary defence technique on from Earth.
00:05:47 --> 00:05:50 DART gave us one clean the change
00:05:50 --> 00:05:53 in the orbital period. What it couldn't tell
00:05:53 --> 00:05:55 us is how much of that change came from the
00:05:55 --> 00:05:58 spacecraft itself and how much came from the
00:05:58 --> 00:06:00 debris Dart blasted off the surface.
00:06:01 --> 00:06:03 When material flies off one way, the asteroid
00:06:03 --> 00:06:06 recoils the other way. A bit like rocket
00:06:06 --> 00:06:09 exhaust. That extra push depends on
00:06:09 --> 00:06:12 what the asteroid is made of and how well it
00:06:12 --> 00:06:12 holds together.
00:06:13 --> 00:06:15 Avery: And to untangle that, you need the mass of
00:06:15 --> 00:06:18 Dimorphos. Exactly. Without the
00:06:18 --> 00:06:21 mass, you can't turn. The orbit changed by
00:06:21 --> 00:06:24 33 minutes into the impact, delivered
00:06:24 --> 00:06:27 this much momentum. And this much of it was a
00:06:27 --> 00:06:29 bonus from the ejecta. That ratio
00:06:29 --> 00:06:32 is the number a future mission would need if
00:06:32 --> 00:06:34 a real asteroid were ever heading our way.
00:06:35 --> 00:06:38 HERA will measure the mass, the shape, the
00:06:38 --> 00:06:41 interior and the impact site, or whatever
00:06:41 --> 00:06:43 Dart actually left behind. Because some
00:06:43 --> 00:06:45 modelling suggests Dimorphos may have been
00:06:45 --> 00:06:48 reshaped rather than simply cratered.
00:06:48 --> 00:06:50 That's why ESA calls it a crash scene
00:06:50 --> 00:06:52 investigation. And, um, HERA doesn't go in
00:06:52 --> 00:06:53 alone.
00:06:53 --> 00:06:55 Anna: It carries two cubesats.
00:06:56 --> 00:06:58 Milani will study composition and dust around
00:06:58 --> 00:07:01 the asteroids. And Juventus carries a
00:07:01 --> 00:07:04 low frequency radarthe first attempt to
00:07:04 --> 00:07:07 sound the inside of an asteroid to find
00:07:07 --> 00:07:10 out whether Dimorphos is solid rock or a
00:07:10 --> 00:07:10 loosely bound
00:07:10 --> 00:07:13 Avery: rubble pile, which matters
00:07:13 --> 00:07:16 enormously for deflection. Hitting a boulder
00:07:16 --> 00:07:17 and hitting a beanbag are very different
00:07:17 --> 00:07:18 experiments.
00:07:19 --> 00:07:21 Anna: Once the braking campaign is done, the plan
00:07:21 --> 00:07:23 is a slow, careful approach.
00:07:24 --> 00:07:27 ESA's Flight Dynamics team describes an early
00:07:27 --> 00:07:30 characterization phase in November and
00:07:30 --> 00:07:32 December at 25 to 30 kilometres
00:07:32 --> 00:07:35 from the asteroids. A detailed phase later in
00:07:35 --> 00:07:38 December down to 10 kilometres, then
00:07:38 --> 00:07:41 early next year getting as close as four
00:07:41 --> 00:07:44 kilometres, and eventually an experimental
00:07:44 --> 00:07:46 phase about one kilometre from Dimorphos.
00:07:47 --> 00:07:49 Avery: And a lot of that it has to do by itself.
00:07:50 --> 00:07:52 Flight Dynamics engineer Michael Mueller
00:07:52 --> 00:07:55 points out that with Rosetta, all the orbit
00:07:55 --> 00:07:57 calculations were done on the ground.
00:07:58 --> 00:08:00 Hera, once the asteroids fill its view, will
00:08:00 --> 00:08:03 track features on their surfaces and work out
00:08:03 --> 00:08:05 where it is on its own.
00:08:05 --> 00:08:08 Anna: A few honest caveats. First,
00:08:08 --> 00:08:11 this is an engineering milestone, not a
00:08:11 --> 00:08:13 science result. The science begins when
00:08:13 --> 00:08:16 Hera is close enough to see the two asteroids
00:08:16 --> 00:08:18 as separate objects, which it can't yet.
00:08:19 --> 00:08:21 Second, big burns don't always go
00:08:21 --> 00:08:24 exactly to plan. That's precisely why
00:08:24 --> 00:08:27 BRM2 is built to correct BRM1.
00:08:28 --> 00:08:30 So if you hear later this week that the first
00:08:30 --> 00:08:32 burn was a little off. That isn't a crisis.
00:08:32 --> 00:08:34 That's the plan working.
00:08:34 --> 00:08:36 Avery: And, um, third, we'll be careful with the
00:08:36 --> 00:08:39 arrival date. ESA describes close
00:08:39 --> 00:08:42 operations beginning in November. And we'll
00:08:42 --> 00:08:45 report HERA as arrived when it actually is,
00:08:45 --> 00:08:46 rather than guess.
00:08:46 --> 00:08:48 Anna: But step back for a second.
00:08:50 --> 00:08:52 Four years ago, a spacecraft hit an
00:08:52 --> 00:08:55 asteroid on purpose. Two years
00:08:55 --> 00:08:58 ago, Hera launched in front of a hurricane.
00:08:58 --> 00:09:01 This week, a European probe starts
00:09:01 --> 00:09:04 breaking beside that same asteroid. And the
00:09:04 --> 00:09:06 first word that the burn worked will come
00:09:06 --> 00:09:09 down to an antenna in the West Australian
00:09:09 --> 00:09:10 wheat belt.
00:09:10 --> 00:09:12 Avery: The the detectives are pulling up to the
00:09:12 --> 00:09:13 crime scene.
00:09:13 --> 00:09:16 Anna: They are, and we'll follow both burns
00:09:17 --> 00:09:19 Avery: from an asteroid to the sun.
00:09:20 --> 00:09:22 When NASA's Parker Solar Probe began diving
00:09:22 --> 00:09:25 close to The sun in 2018, it kept seeing
00:09:25 --> 00:09:28 something odd in the solar wind. The magnetic
00:09:28 --> 00:09:30 field would suddenly kink back on itself,
00:09:30 --> 00:09:33 snapping round almost the wrong way for
00:09:33 --> 00:09:35 seconds or minutes, then flipping back.
00:09:36 --> 00:09:38 Scientists called them switchbacks, and
00:09:38 --> 00:09:40 Parker found them everywhere.
00:09:40 --> 00:09:42 Anna: We last caught up with Parker in September
00:09:42 --> 00:09:45 when it matched its own speed record on its
00:09:45 --> 00:09:46 29th. Close pass.
00:09:47 --> 00:09:50 Avery: Right. And the big argument has been where
00:09:50 --> 00:09:53 switchbacks come from. One camp says
00:09:53 --> 00:09:55 they're born at the sun's surface when
00:09:55 --> 00:09:57 magnetic field lines reconnect. The other
00:09:57 --> 00:10:00 says they grow on the way out from waves and
00:10:00 --> 00:10:02 turbulence in the solar wind itself.
00:10:02 --> 00:10:04 Anna: So which is it?
00:10:05 --> 00:10:07 Avery: According to a paper published last Thursday
00:10:07 --> 00:10:09 in Nature Astronomy, the both
00:10:10 --> 00:10:13 Jesse Coburn of Francis CNRS led a team
00:10:13 --> 00:10:15 using Europe's Solar orbiter, which on the
00:10:15 --> 00:10:18 2nd of March, 2022, at a little over
00:10:18 --> 00:10:21 half Earth's distance from the sun, flew
00:10:21 --> 00:10:22 straight through an unusually large
00:10:22 --> 00:10:25 switchback. It took about an hour and a half
00:10:25 --> 00:10:25 to cross.
00:10:26 --> 00:10:28 Anna: And because it was so big, Solar
00:10:28 --> 00:10:31 Orbiter's solar wind analyzer could
00:10:31 --> 00:10:33 properly sample the heavy particles inside
00:10:33 --> 00:10:36 it, oxygen and carbon ions, which
00:10:36 --> 00:10:38 most switchbacks are too brief to catch.
00:10:39 --> 00:10:42 Avery: Those ions work like a fingerprint. How many
00:10:42 --> 00:10:44 electrons an oxygen or carbon atom has lost
00:10:44 --> 00:10:47 get set in the hot corona and then frozen
00:10:47 --> 00:10:50 in as the wind leaves the mix inside. This
00:10:50 --> 00:10:53 switchback could only have formed in hot
00:10:53 --> 00:10:55 closed magnetic loops at the surface of the
00:10:55 --> 00:10:57 sun at around a million degrees.
00:10:58 --> 00:11:01 Anna: Closed loops. But the solar wind
00:11:01 --> 00:11:03 streams out along open field lines.
00:11:04 --> 00:11:06 Avery: That's the key. The team calls it a smoking
00:11:06 --> 00:11:09 gun for interchange reconnection. An open
00:11:09 --> 00:11:12 field line runs into a closed loop. They snap
00:11:12 --> 00:11:15 and reconnect, and plasma that was trapped in
00:11:15 --> 00:11:17 the loop is suddenly released into space,
00:11:17 --> 00:11:19 carrying a kink with it. Combining the
00:11:19 --> 00:11:21 spacecraft's measurements with a new model
00:11:21 --> 00:11:23 and imagery from NASA's Solar Dynamics
00:11:23 --> 00:11:26 Observatory, they trace this switchback back
00:11:26 --> 00:11:27 to its source region.
00:11:28 --> 00:11:30 Anna: So where do the waves come in
00:11:30 --> 00:11:31 afterwards?
00:11:32 --> 00:11:34 Avery: Co author Stephanie Yardley at Northumbria
00:11:34 --> 00:11:37 University says they also see signs of waves
00:11:37 --> 00:11:39 and turbulence, but likely only once the
00:11:39 --> 00:11:42 switchback has left the Sun. Reconnection
00:11:42 --> 00:11:44 makes it. Turbulence carries and shapes it.
00:11:45 --> 00:11:47 The two theories were describing different
00:11:47 --> 00:11:48 stages of the same thing's life.
00:11:49 --> 00:11:51 Anna: One disclosure, uh, the crossing happened in
00:11:51 --> 00:11:54 March 2022. The paper is new this
00:11:54 --> 00:11:56 week, but the data are four and a half years
00:11:56 --> 00:11:58 old, which is normal for this kind of
00:11:58 --> 00:11:59 forensic work.
00:12:00 --> 00:12:02 Avery: And it matters. Beyond the puzzle,
00:12:02 --> 00:12:04 understanding how the corona heats up and
00:12:04 --> 00:12:07 launches the solar wind sits underneath every
00:12:07 --> 00:12:10 space weather forecast. ESA project
00:12:10 --> 00:12:12 scientist Daniel Mueller makes the point that
00:12:12 --> 00:12:14 no other spacecraft has the combination of
00:12:14 --> 00:12:17 closeness and the right instruments to make
00:12:17 --> 00:12:18 this connection.
00:12:18 --> 00:12:21 Anna: It's a nice example of two spacecraft working
00:12:21 --> 00:12:23 as a pair of Parker diving in close to
00:12:23 --> 00:12:26 find the phenomenon and solar orbiters
00:12:26 --> 00:12:28 standing a little further back with the tools
00:12:28 --> 00:12:29 to trace where it came from.
00:12:31 --> 00:12:33 YADFT In August of
00:12:33 --> 00:12:36 1181, astronomers in China and
00:12:36 --> 00:12:39 Japan recorded a guest star in the part
00:12:39 --> 00:12:42 of the sky we call Cassiopeia. It stayed
00:12:42 --> 00:12:45 visible for about six months, then faded
00:12:45 --> 00:12:47 away. It's one of only five
00:12:47 --> 00:12:50 supernovae in our galaxy that people are
00:12:50 --> 00:12:52 known to have seen with the naked eye before
00:12:52 --> 00:12:54 Avery: the telescope, the others being
00:12:55 --> 00:12:57 1006, 1054, which
00:12:57 --> 00:13:00 gave us the Crab Nebula, 1572
00:13:00 --> 00:13:02 and, um, 1604.
00:13:02 --> 00:13:05 Anna: And for centuries, nobody could find what the
00:13:05 --> 00:13:07 1181 star left behind.
00:13:08 --> 00:13:11 Then in 2013, an amateur
00:13:11 --> 00:13:13 astronomer, Dana Patchik, combing through
00:13:13 --> 00:13:16 archival data from NASA's WISE infrared
00:13:16 --> 00:13:19 survey, found a faint nebula in he
00:13:19 --> 00:13:22 catalogued as his 30th discovery PA
00:13:22 --> 00:13:24 AH30, Patchk 30.
00:13:25 --> 00:13:27 Its age and brightness line up with the
00:13:27 --> 00:13:30 1181 event, and it's now the leading
00:13:30 --> 00:13:33 candidate for that remnant, about 7 light
00:13:33 --> 00:13:35 years away. And it's very
00:13:35 --> 00:13:38 strange. Earlier images showed long,
00:13:38 --> 00:13:40 straight filaments radiating from a hot
00:13:40 --> 00:13:43 central star, like a, uh, dandelion seed head
00:13:43 --> 00:13:46 or a frozen firework. Nothing like
00:13:46 --> 00:13:48 any other supernova remnant.
00:13:48 --> 00:13:50 Avery: And there's a star in the middle that
00:13:50 --> 00:13:52 arguably shouldn't be there.
00:13:52 --> 00:13:55 Anna: That's the other oddity. PA 30
00:13:55 --> 00:13:58 is thought to be the remnant of a Type 1
00:13:58 --> 00:14:00 axe supernova, a weak,
00:14:00 --> 00:14:03 incomplete thermonuclear explosion of a white
00:14:03 --> 00:14:05 dwarf that failed to destroy the star.
00:14:06 --> 00:14:08 What's left at the centre is sometimes called
00:14:08 --> 00:14:11 a zombie star, and it's blowing an
00:14:11 --> 00:14:12 extremely fast window.
00:14:13 --> 00:14:15 Avery: So what's new?
00:14:15 --> 00:14:17 Anna: A team led by Timms Cunningham with
00:14:17 --> 00:14:20 Hilaria Chayazo among the co authors.
00:14:20 --> 00:14:23 Published in the astrophysical journal on
00:14:23 --> 00:14:26 6 October using the Gemini north
00:14:26 --> 00:14:28 telescope on Mauna Kea. They m observed
00:14:28 --> 00:14:31 over six nights in July and August last year,
00:14:32 --> 00:14:34 mainly through a filter that isolates glowing
00:14:34 --> 00:14:37 sulphur. And the filaments aren't smooth
00:14:37 --> 00:14:40 streaks. Each one is a chain of
00:14:40 --> 00:14:42 knots strung like pearls.
00:14:43 --> 00:14:45 Avery: How big are the pearls?
00:14:45 --> 00:14:47 Anna: Each knot is roughly 100 billion
00:14:47 --> 00:14:50 kilometres across. That's wide enough to hold
00:14:50 --> 00:14:53 the orbits of all eight planets about 10
00:14:53 --> 00:14:55 times over. And they're strikingly uniform in
00:14:55 --> 00:14:57 size along the filaments.
00:14:57 --> 00:15:00 Avery: Uniform knots are a big clue for theorists.
00:15:01 --> 00:15:03 Something is setting that size.
00:15:03 --> 00:15:06 Anna: It is. And here's the honest
00:15:06 --> 00:15:09 bit. The paper shows the knots but
00:15:09 --> 00:15:11 doesn't settle what made them. There are
00:15:11 --> 00:15:14 competing ideas. One where the central star's
00:15:14 --> 00:15:17 wind sculpts the filaments. Another where the
00:15:17 --> 00:15:19 ejecta cooled unusually quickly.
00:15:19 --> 00:15:22 Gemini has given theorists a uh, much sharper
00:15:22 --> 00:15:25 target. Not a final answer. The
00:15:25 --> 00:15:27 team also found the central star shows little
00:15:27 --> 00:15:30 sideways recoil from the explosion. The which
00:15:30 --> 00:15:33 is one more constraint any model has to meet.
00:15:33 --> 00:15:36 Avery: Two disclosures. The observations are from
00:15:36 --> 00:15:39 mid-2025 and were published this month.
00:15:39 --> 00:15:42 And for our Southern listeners. PA30 sits
00:15:42 --> 00:15:45 in the far northern sky at a declination of
00:15:45 --> 00:15:48 about 67 degrees. It never
00:15:48 --> 00:15:50 rises from Cygni, so this
00:15:50 --> 00:15:53 Anna: one belongs to the north. Although ah, this
00:15:53 --> 00:15:55 faintness. It's a big telescope target for
00:15:55 --> 00:15:56 everyone.
00:15:56 --> 00:15:59 What I love is the chain of people across
00:15:59 --> 00:16:01 time court astronomers in
00:16:01 --> 00:16:04 1181, an amateur in 2013
00:16:04 --> 00:16:07 and a spectrograph on a Hawaiian volcano in
00:16:07 --> 00:16:09 2025 all looking at the same object.
00:16:10 --> 00:16:13 Avery: Staying with violence, but going back to the
00:16:13 --> 00:16:15 very beginning of planetary systems.
00:16:15 --> 00:16:18 Our moon is thought to have formed when a
00:16:18 --> 00:16:21 Mars sized body slammed into the young Earth.
00:16:21 --> 00:16:23 Collisions like that should be routine while
00:16:23 --> 00:16:26 rocky planets are being assembled. So why
00:16:26 --> 00:16:28 don't we see their aftermath more often?
00:16:29 --> 00:16:30 Anna: Because the evidence doesn't last.
00:16:31 --> 00:16:34 Avery: Right. NASA's retired Spitzer
00:16:34 --> 00:16:36 telescope found a rare class of system called
00:16:36 --> 00:16:39 extreme debris discs. Young stars with
00:16:39 --> 00:16:42 huge amounts of warm dust close in roughly
00:16:42 --> 00:16:45 where rocky planets orbit. They turn up
00:16:45 --> 00:16:47 around only about 1% of young stars.
00:16:48 --> 00:16:50 Now a team led by Kate Hsu at the Space
00:16:50 --> 00:16:52 Science Institute in Boulder has assembled
00:16:52 --> 00:16:55 the largest sample yet 21 of
00:16:55 --> 00:16:58 them. 16 observed with Webb's mid infrared
00:16:58 --> 00:17:01 instrument and 5 from Spitzer's archive. The
00:17:01 --> 00:17:03 paper appeared in the astrophysical journal
00:17:03 --> 00:17:05 on the 1st of October.
00:17:05 --> 00:17:07 Anna: And what did they have in common?
00:17:07 --> 00:17:10 Avery: Three things. Smaller dust grains than
00:17:10 --> 00:17:13 ordinary debris discs. A lot of warm dust
00:17:13 --> 00:17:16 Packed close to the star and infrared
00:17:16 --> 00:17:18 brightness that changes irregularly. Then
00:17:18 --> 00:17:21 webb spectra let the team read the minerals
00:17:21 --> 00:17:24 and the discs split into two families,
00:17:24 --> 00:17:27 silica rich and silica poor. About a
00:17:27 --> 00:17:29 third are silica rich and
00:17:29 --> 00:17:31 Anna: silica is the interesting one.
00:17:31 --> 00:17:34 Avery: Silica rich dust points to impacts
00:17:34 --> 00:17:37 violent enough to vaporise rock and the
00:17:37 --> 00:17:39 team's interpretation is that those come from
00:17:39 --> 00:17:42 collisions between planetary embryos around
00:17:42 --> 00:17:45 the size of Mars. Co author Agnes
00:17:45 --> 00:17:48 Kolsbal of Hungary's Konkoly Observatory put
00:17:48 --> 00:17:50 it neatly. We have no other way to study
00:17:50 --> 00:17:53 these planetary embryos directly because they
00:17:53 --> 00:17:54 are too small.
00:17:54 --> 00:17:56 Anna: Does it make a prediction?
00:17:56 --> 00:17:59 Avery: It does. If silica rich discs come
00:17:59 --> 00:18:01 from that early embryo smashing
00:18:01 --> 00:18:04 phase, you shouldn't find them around older
00:18:04 --> 00:18:07 stars. So older extreme debris
00:18:07 --> 00:18:09 discs should all be silica poor. That's
00:18:09 --> 00:18:12 testable as the sample grows. Caveats
00:18:13 --> 00:18:16 21 Systems is the biggest sample yet,
00:18:16 --> 00:18:19 but still small and marsh sized
00:18:19 --> 00:18:21 embryos is what the composition is consistent
00:18:21 --> 00:18:24 with, not a direct measurement of the bodies
00:18:24 --> 00:18:26 involved. It links back nicely to our
00:18:26 --> 00:18:29 story in episode 188 on uh, simulations that
00:18:29 --> 00:18:31 can build a moon within hours of a giant
00:18:31 --> 00:18:32 impact.
00:18:32 --> 00:18:35 This is what the far side of that kind of
00:18:35 --> 00:18:37 collision might look like from light years
00:18:37 --> 00:18:37 away.
00:18:38 --> 00:18:40 Anna: A quick one before the sky. On Sunday
00:18:40 --> 00:18:43 the 11th, NASA's Perseverance
00:18:43 --> 00:18:45 rover became the farthest driving vehicle
00:18:45 --> 00:18:48 ever on another world. A 91
00:18:48 --> 00:18:50 metre drive took its odometer to
00:18:50 --> 00:18:53 45.22 kilometres, just past
00:18:53 --> 00:18:56 the 45.16 set by Opportunity,
00:18:56 --> 00:18:59 which explored Mars from 2004 to
00:18:59 --> 00:19:00 2018.
00:19:01 --> 00:19:03 Avery: Opportunity took nearly 15 years to get
00:19:03 --> 00:19:06 there. Perseverance did it in five and a half
00:19:06 --> 00:19:08 on its 2006 Martian Day.
00:19:08 --> 00:19:11 Anna: It had already passed the moon's records on
00:19:11 --> 00:19:14 the way the Apollo 17 cruise rover at
00:19:14 --> 00:19:16 about 35.7 kilometres and the
00:19:16 --> 00:19:19 Soviet Lunokhod 2 at about 39.
00:19:19 --> 00:19:21 Most of the credit goes to self driving.
00:19:22 --> 00:19:25 Perseverance has covered more than 90% of its
00:19:25 --> 00:19:28 distance on autonav, imaging the ground as it
00:19:28 --> 00:19:30 rolls, building a 3D hazard map and choosing
00:19:30 --> 00:19:33 its own path. Opportunity managed about
00:19:33 --> 00:19:35 5% thatby and it isn't
00:19:35 --> 00:19:36 finished.
00:19:37 --> 00:19:39 Avery: Project manager Stephen Lee notes the
00:19:39 --> 00:19:41 original mission called for no more than
00:19:41 --> 00:19:44 about 20 kilometres of driving and NASA has
00:19:44 --> 00:19:46 just approved a first extension running to
00:19:46 --> 00:19:49 roughly the end of 2028. Right now
00:19:49 --> 00:19:52 the rover is on the western rim of Jezero in
00:19:52 --> 00:19:54 a region called Lac d', Sharme, heading for
00:19:54 --> 00:19:57 an area called Idubi to look for traces of
00:19:57 --> 00:19:59 ancient hydrothermal systems. That's the
00:19:59 --> 00:20:01 crater rim story we covered in episode two.
00:20:01 --> 00:20:01 Hundred.
00:20:02 --> 00:20:05 Anna: And every metre of it gets reported home
00:20:05 --> 00:20:07 through NASA's Deep Space Network, including
00:20:07 --> 00:20:10 the dishes at Tidbinbilla outside Canberra.
00:20:10 --> 00:20:13 Avery: Time to look up. And let's start with
00:20:13 --> 00:20:16 tomorrow evening, Wednesday the 14th, when
00:20:16 --> 00:20:18 the Crescent moon visits Antares, the red
00:20:18 --> 00:20:20 heart of Scorpius.
00:20:20 --> 00:20:21 Anna: Google gets the better view.
00:20:22 --> 00:20:25 Avery: It's genuinely split from Sydney.
00:20:25 --> 00:20:28 At Sunset just after 7, the moon is
00:20:28 --> 00:20:30 about 15% lit and sits a
00:20:30 --> 00:20:33 comfortable 41 degrees up in the west with
00:20:33 --> 00:20:36 Antares about 7 degrees away. High,
00:20:36 --> 00:20:39 dark and easy. And the moon stays up for
00:20:39 --> 00:20:40 nearly four hours.
00:20:41 --> 00:20:44 Anna: And in the north, tighter but much
00:20:44 --> 00:20:47 Avery: lower from New York at sunset about
00:20:47 --> 00:20:50 quarter past six, the moon is only 14 degrees
00:20:50 --> 00:20:53 up with Antares just over a degree
00:20:53 --> 00:20:56 away from Los Angeles the moon is about
00:20:56 --> 00:20:58 19° up with Antares around
00:20:58 --> 00:21:01 2° off, so northern listeners
00:21:01 --> 00:21:03 get the closer pairing. But you'll need a
00:21:03 --> 00:21:06 clear low western horizon soon after sunset
00:21:07 --> 00:21:09 from London it's right down on the
00:21:09 --> 00:21:11 horizon, which makes it a tough one.
00:21:12 --> 00:21:14 Anna: Any chance of the moon actually covering
00:21:14 --> 00:21:15 Antares?
00:21:16 --> 00:21:18 Avery: Not from any of our four cities. We
00:21:18 --> 00:21:21 checked and um, the closest approaches happen
00:21:21 --> 00:21:24 either in daylight or with the pair below the
00:21:24 --> 00:21:25 horizon.
00:21:25 --> 00:21:27 Anna: What else is up in the evening?
00:21:27 --> 00:21:30 Avery: For the south, Mercury is still giving its
00:21:30 --> 00:21:33 best show of the year. It's 24 degrees up
00:21:33 --> 00:21:36 at sunset from Sydney and sets about two
00:21:36 --> 00:21:38 hours after the Sun. Look lower in the west
00:21:38 --> 00:21:41 on the Moon. From New York it's only about 7
00:21:41 --> 00:21:44 degrees up and from London barely 3.
00:21:45 --> 00:21:48 And Venus is leaving us. It's heading for
00:21:48 --> 00:21:50 inferior conjunction passing between Earth
00:21:50 --> 00:21:52 and the sun around the 24th.
00:21:53 --> 00:21:55 From Sydney it's still about 15 degrees up at
00:21:55 --> 00:21:58 sunset, so catch it this week. From
00:21:58 --> 00:22:01 New York and London it's already gone. And
00:22:01 --> 00:22:03 from Los Angeles tomorrow it's under a degree
00:22:03 --> 00:22:06 up at sunset, which means it's effectively
00:22:06 --> 00:22:07 finished there.
00:22:07 --> 00:22:08 Anna: And Saturn?
00:22:09 --> 00:22:12 Avery: Saturn is just past opposition, rising
00:22:12 --> 00:22:15 around sunset and up all night. It's low
00:22:15 --> 00:22:17 in the east in the early evening for everyone
00:22:17 --> 00:22:19 and and highest around midnight.
00:22:19 --> 00:22:22 Anna: Now, uh, give the north something good.
00:22:23 --> 00:22:26 Avery: The pre dawn sky belongs to the north.
00:22:26 --> 00:22:29 On Thursday morning at nautical dawn, Mars
00:22:29 --> 00:22:32 and Jupiter are about 12 degrees apart and
00:22:32 --> 00:22:35 riding high. Mars is almost 59
00:22:35 --> 00:22:37 degrees up from Los Angeles and 56 from New
00:22:37 --> 00:22:40 York, with Jupiter in the mid-40s.
00:22:40 --> 00:22:43 From Sydney they're only about 23 and 18
00:22:43 --> 00:22:46 degrees. The pair keeps closing towards a
00:22:46 --> 00:22:48 close meeting in mid November.
00:22:48 --> 00:22:49 Anna: Moon face us.
00:22:50 --> 00:22:52 Avery: First quarter is Sunday the 18th at
00:22:52 --> 00:22:55 1612 UTC. That's midday
00:22:55 --> 00:22:57 Sunday on the US East Coast.
00:22:58 --> 00:23:00 Nine in the morning in Los Angeles and 3:12
00:23:00 --> 00:23:03 on Monday. Morning in Sydney. Full Moon
00:23:03 --> 00:23:06 follows On the 26th, the Hunter's Moon for
00:23:06 --> 00:23:07 northern listeners and a
00:23:07 --> 00:23:10 Anna: heads up for next week, the Orionids.
00:23:10 --> 00:23:12 Avery: The October shower made of dust from Hallie's
00:23:12 --> 00:23:15 Comet peak on the night of the 21st into the
00:23:15 --> 00:23:16 22nd.
00:23:16 --> 00:23:19 The moon will be around 80% lit, but it sets
00:23:19 --> 00:23:22 before 4 in the morning in all four of our
00:23:22 --> 00:23:24 cities, leaving a dark window before dawn
00:23:24 --> 00:23:27 at 4am The Radiant near Orion's
00:23:27 --> 00:23:30 raised club is about 60 to 66 degrees
00:23:30 --> 00:23:33 up from New York and Los Angeles, about 51
00:23:33 --> 00:23:36 from London and about 37 from Sydney,
00:23:36 --> 00:23:38 so the north is favoured. But this is a
00:23:38 --> 00:23:41 shower everyone can see under dark skies,
00:23:41 --> 00:23:44 perhaps a couple of dozen an hour at best.
00:23:44 --> 00:23:47 Anna: And our standing Safety note Always
00:23:47 --> 00:23:48 never
00:23:48 --> 00:23:50 Avery: look directly at the sun with your eyes or
00:23:50 --> 00:23:53 through binoculars, a camera or a telescope.
00:23:53 --> 00:23:56 If you ever observe the sun, including during
00:23:56 --> 00:23:58 a, uh, partial eclipse, use only certified
00:23:58 --> 00:24:01 solar viewers or filters that meet the ISO
00:24:01 --> 00:24:04 123122 international
00:24:04 --> 00:24:05 safety standard.
00:24:05 --> 00:24:08 Check them for scratches or damage first and
00:24:08 --> 00:24:11 supervise children. Ordinary sunglasses are
00:24:11 --> 00:24:14 not safe. With two solar eclipses coming
00:24:14 --> 00:24:17 in 2027, it's worth getting proper filters
00:24:17 --> 00:24:18 well ahead of time.
00:24:18 --> 00:24:20 Anna: That's Astronomy daily for Tuesday
00:24:21 --> 00:24:24 13th October. HERA's first
00:24:24 --> 00:24:26 braking burn is on Thursday and we'll bring
00:24:26 --> 00:24:29 you the result once ESA confirms it.
00:24:29 --> 00:24:32 Avery: Show notes, sources and every link are at
00:24:32 --> 00:24:35 astronomydaily IO where you can also sign up
00:24:35 --> 00:24:36 for the newsletter and send us questions
00:24:36 --> 00:24:39 through the contact form. Listener questions
00:24:39 --> 00:24:40 have shaped more than one segment on this
00:24:40 --> 00:24:41 show.
00:24:41 --> 00:24:44 Anna: We are AstroDaily Pod on social media
00:24:44 --> 00:24:46 and if you're enjoying this show, a uh,
00:24:46 --> 00:24:48 rating or review in your podcast app
00:24:48 --> 00:24:50 genuinely helps other people find us.
00:24:51 --> 00:24:53 Avery: Astronomy AstroDailyPod is part of the
00:24:53 --> 00:24:55 bites.com podcast network. I'm M.
00:24:56 --> 00:24:56 Avery.
00:24:56 --> 00:24:59 Anna: And I'm Anna. Clear Skies
00:25:00 --> 00:25:01 Astronomy Day
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00:25:06 --> 00:25:06 Love.
00:25:11 --> 00:25:11 Story.
00:25:19 --> 00:25:20 For soul.